The arthropodicidal and acaricidal oxazolines and thiazolines of this invention are characterized by a fused ring system or a monocyclic heterocycle. This ring distinguishes the compounds of this invention from those of EP 345,775 and EP 432,661. N. Ardabilchi, et al., J. Chem. Soc, Perkin Trans I (1979), 539-543 discloses 4,5-dihydro-4-methyl-5-(1-naphthalenyl)-2-phenyloxazole but does not disclose any arthropodicidal utility.